Method and device for generating and detecting a fingerprint functioning as a trigger marker in a multimedia signal

ABSTRACT

A device is configured to perform a method that detects a trigger marker for an action corresponding to a segment of a multimedia signal. A fingerprint is generated based on the segment of the multimedia signal at a trigger time point. The generated fingerprint is stored in a database and communicated to the device. During playback of the multimedia signal, fingerprints of segments of the multimedia signal are generated and matched against fingerprints in the database. When a match is found, one or more associated actions for the segment are retrieved by the device. The trigger time point may be determined as a time point near or at the segment of the multimedia signal with the matched fingerprint. In this way, trigger markers for actions may be enabled without modifying the multimedia signal.

This application is a Continuation of U.S. patent application Ser. No.15/164,605, filed May 25, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/659,044, filed Mar. 16, 2015, which is aContinuation of U.S. patent application Ser. No. 14/151,879, filed Jan.10, 2014 and issued on Jun. 23, 2015 as U.S. Pat. No. 9,066,114, whichis a Continuation of U.S. patent application Ser. No. 13/220,267, filedAug. 29, 2011 and issued on Feb. 25, 2014 as U.S. Pat. No. 8,660,267,which is a Continuation of U.S. patent application Ser. No. 10/564,297,filed Jan. 10, 2006 and issued on Sep. 13, 2011 as U.S. Pat. No.8,020,000, which is a U.S. National Stage Filing from InternationalPatent Application Serial No. PCT/IB2004/051128, filed Jul. 5, 2004, andpublished on Jan. 20, 2005 as WO 2005/006758, which claims priority toEP Application No. 03102116.5, filed Jul. 11, 2003, which applicationsare incorporated by reference herein in their entirety.

The invention relates to a method, and a corresponding device, ofdetecting trigger instants/information in a multimedia signal. Theinvention also relates to a method, and a corresponding device, ofassociating trigger information with a multimedia signal. Further, theinvention relates to a computer readable medium having stored thereoninstructions for causing one or more processing units to execute themethod according to the invention.

A current trend is to enhance passive television viewing and/or musiclistening on a given playback device by creating more interactiveprograms and/or listening experiences or by “connecting” externalactions to a piece of video and/or audio content. As one simple example,a commercial can be enhanced by embedding a URL to a web site withfurther information, where the URL can be extracted and retrieved by theplayback device. In order to facilitate such a function it is necessaryto enable a reliable detection of time points in a television program, amovie, a music piece, etc. where such additional information isrelevant.

Examples of situations where such additional information is useful orinteresting in connection with a broadcast program are:

-   -   trigg&link: (see e.g. W. ten Kate et.al. trigg&link—A new        dimension in television program making”, Lecture Notes in        computer Science, vol. 1242, pp51-65, Springer, 1997) trigg&link        allows interactivity in television programs. In addition to the        normal program, additional information concerning specific        segments of the program is available to the viewer through a        different distribution channel. At the start of a given segment        that is associated with an enhancement (additional information)        an icon is displayed, alerting the viewer that additional        information may be viewed on his TV. For instance, at the        appearance of an actor in a movie, some biographic data of the        actor may be made available. In the user terminal (e.g. a set        top box, etc.) the icons are overlayed on the video at the        relevant time instants, thereby requiring these instants to have        been indicated in the video stream.    -   Local Insertion: During a national broadcast, specific parts of        the program may be replaced by a regional program in some        regions. For instance, some advertisements may be replaced by        advertisements for local shops, or, in a news show some regions        may have their local weather forecast rather than the national        one. The national program producer can indicate which segments        are suitable for such local insertion. At the local        redistribution site (e.g. at the cable head-end), the indicated        segments may be replaced by local content.

In both of the above situations, it is necessary to mark or associatespecific time instants in the video stream at which additionalinformation should be available. At these time instants the receivershould be triggered to perform or provide some kind of action. This maybe done by such mechanisms as DSM-CC in MPEG/DVB. However, this requiresthe broadcaster's cooperation to insert these triggers thereby making anenhancement service provider dependent on the broadcaster.

One previously known way of performing time marking in a video stream ise.g. using fields of the MPEG transport stream structure that can beused to hold the marking information.

Another previously known way is using a blanking interval. In analogdistribution, the marking information can be embedded in the verticalblanking interval or in the inactive video lines.

Both of the above known ways need the cooperation of all actors in thebroadcast chain to make sure that the marking information is notdestroyed before the signal arrives at its destination. For instance, incase of the MPEG solution, a re-multiplexing operation could easilyremove information that is written in the user data fields in thestream. Moreover, every decoding and successive re-encoding step wouldcertainly not retain this information. In case of the use of thevertical blanking for carrying the trigger information, the situation iseven more difficult, as actors in the broadcast chain might write otherinformation at the same position (the vertical blanking is used for manythings and there is no uniform agreement about the control over usage ofthe blanking interval). Also, standards converters (like PAL-NTSC) andother equipment in the broadcast chain may not retain all information inthe vertical blanking interval.

Yet another way is using watermarking. A watermark may be embedded inthe video frames at the relevant time instants. The Philips WatercastSystem is, among others, being sold for this purpose. A disadvantage ofwatermarking is the fact that it necessarily changes the video/audio.

It is an object of the invention to provide a method and correspondingdevice of relating one or more trigger actions with a multimedia signaland corresponding method and device for detecting one or more triggeractions in a multimedia signal that solves the above-mentioned problems.A further object is to provide this in a simple and efficient way.Another object is to enable simple, reliable and accurate localisationof a given part of a multimedia signal. A further object is to enabledetection of trigger actions without modifying the multimedia signal.This is achieved by a method (and corresponding device) of relating oneor more trigger actions with a multimedia signal, the method comprisingthe steps of

-   -   providing at least one trigger time point and for each trigger        time point providing at least one representation of least one        associated trigger action, where each trigger time point        indicates a time point of the multimedia signal for which the at        least one associated trigger action is to be available during        playback of the multimedia signal, and    -   for each given trigger time point deriving a fingerprint on the        basis of a. segment of the multimedia signal, where the segment        of the multimedia signal is unambiguously related with the given        trigger time point,    -   and by a method (and corresponding device) of detecting one or        more trigger actions in a multimedia signal, the method        comprising the steps of:        -   generating a fingerprint stream on the basis of the            multimedia signal,        -   comparing a segment of the fingerprint stream with one or            more fingerprints stored in a second database in order to            determine if a match exists or not between the segment and a            fingerprint in the second database, the second database            further comprising for each stored fingerprint at least one            representation of at least one associated action, and        -   if a match exists retrieving the at least one representation            of the at least one associated action associated with the            matching fingerprint.

In this way, a simple and efficient way of handling time markers in amultimedia signal for given actions is obtained. A fingerprint therebyserves as a trigger of a particular action, event, etc. associated witha particular point in time of the multimedia signal. Further, this isenabled without the multimedia signal needing to be modified.Additionally, the time marking detection is time independent as it isdependent on the specific content of the multimedia signal only therebyavoiding problems if a multimedia signal being a television program orthe like is delayed.

A fingerprint of a multimedia object/content/signal is a representationof perceptual features of the object/content/signal part in question.Such fingerprints are sometimes also known as “(robust) bashes”. Morespecifically, a fingerprint of a piece of audio or video is anidentifier which is computed over that piece of audio or video and whichdoes not change even if the content involved is subsequently transcoded,filtered or otherwise modified.

Preferably, the derived fingerprint is an audio and/or videofingerprint. Alternatively, animations and/or streaming text, etc. isused as a source for creating a fingerprint.

Advantageous embodiments of the methods and devices according to thepresent invention are defined in the sub-claims.

Further, the invention also relates to a computer readable medium havingstored thereon instructions for causing one or more processing units toexecute the method according to the present invention.

FIG. 1a schematically illustrates generation of fingerprint(s) used astrigger marker(s) according to the present invention.

FIG. 1b schematically illustrates detection and use of fingerprint(s) astrigger marker(s) according to the present invention.

FIG. 2 illustrates a schematic block diagram of a fingerprint generationdevice according to the present invention;

FIG. 3 illustrates a schematic block diagram of a playback devicedetecting and using fingerprints according to the present invention;

FIG. 4 illustrates one example of tables/records according to thepresent invention.

FIG. 1a schematically illustrates generation of fingerprint (s) used astrigger marker(s) according to the present invention.

Shown is a digital or analog multimedia signal (101) comprising videoand/or audio information/content, where one or more ‘trigger’ actions(forth denoted actions) is to be associated/related with the multimediasignal (101) at certain given ‘trigger’ time points (forth denoted timepoints). The one or more actions associated with each time point is tobe available, i.e. triggered, at that given particular time point(T_(n); T_(n+1)) during playback on a playback device. The notation‘(T_(n); T_(n+1))’for a given time point signifies that the time pointmay be either the shown time point T_(n) or the shown time point T_(n+1)or in general any suitable (not shown) time point of the signal (101).The associated actions of multiple time points may be the same,different and/or a mix thereof.

The action(s) to be presented/triggered at a given time point may e.g.comprise retrieving and displaying additional information on a display(e.g. presenting biography data for an actor being shown by themultimedia signal, presenting a selectable URL to a web site containingadditional information, etc.), retrieving and playing additionalinformation via a speaker, playing another multimedia signal instead ofsaid multimedia signal (101) for a predetermined or variable period oftime (e.g. a local weather forecast, a local commercial, etc.) and/orthe like. Other examples of action(s) are e.g. stopping/pausing, e.g.

temporarily, display/play, executing other control commands, and/orpreparing the system for user input(s), e.g. once the trigger action isexecuted the system waits (for some time) for a specific action of theuser. If the trigger action was not executed, the user input will nothave any influence. For example, in interactive games the user may onlysubmit his answer after the trigger action has fired/been executed.

For each time point (T_(n); T_(n+1)) a fingerprint (102) is generated onthe basis of a part, segment. etc. (forth denoted segment) of themultimedia signal (101), where the segment of the multimedia signal(101) is unambiguously related with the given time point (T_(n);T_(n+1)). Preferably, the segment of the multimedia signal (101) isunambiguously related with the given time point (T_(n); T_(n+1)) byletting the segment of the multimedia signal (101) ending substantiallyat the given time point (T_(n); T_(n+1)). In alternative embodiments,the segment of the multimedia signal (101) may start substantially atthe given time point (T_(n); T_(n+1)), the segment of the multimediasignal (101) is starting or ending at a predetermined distance before orafter the given trigger time point (T_(n); T_(n+1)), or the given timepoint (T_(n); T_(n+1)) may be at a predetermined time point between astart and an end of the segment of the multimedia signal (101).

The size of the fingerprints and/or the segments may both be of apredetermined fixed size or alternatively of a variable size.

One method for computing a robust fingerprint is described in Europeanpatent application 01200505.4, although of course any method forcomputing a robust fingerprint can be used.

European patent application 01200505.4 describes a method that generatesrobust fingerprints for multimedia content such as, for example, audioclips, where the audio clip is divided in successive (preferablyoverlapping) time intervals. For each time interval, the frequencyspectrum is divided in bands. A robust property of each band (e.g.energy) is computed and represented by a respective fingerprint bit.

Multimedia content is thus represented by a fingerprint comprising aconcatenation of binary values, one for each time interval. Thefingerprint does not need to be computed over the whole multimediacontent, but can be computed when a portion of a certain length has beenreceived. There can thus be plural fingerprints for one multimediacontent, depending on which portion is used to compute the fingerprintover.

Further, video fingerprinting algorithms are known, e.g. from thefollowing disclosure: Job Oostveen, Ton Kalker, Jaap Haitsma: “FeatureExtraction and a Database Strategy for Video Fingerprinting”. 117-128.IN: Shi-Kuo Chang, Zhe Chen, Suh-Yin Lee (Eds.): Recent Advances inVisual Information Systems, 5th International Conference, VISUAL 2002Hsin Chu, Taiwan, Mar. 11-13, 2002, Proceedings. Lecture Notes inComputer Science 2314 Springer 2002.

According to the present invention, a fingerprint (102) is generated foreach time point on the basis of a given segment of the multimedia signal(101) at or near the specific time point.

In this way, a given fingerprint (102) is a trigger marker enabling avery accurate and very precise location of a given time point of thesignal (101) without using the specific time point but instead using (asegment of) the signal. Further, this is enabled without changing thesignal. For video fingerprinting the localisation is typically frameaccurate, at least as long as any distortion of the video signal is nottoo severe.

After a fingerprint (102) has been generated it is stored for later usein a database, memory, storage and/or the like.

There are several advantages in storing fingerprints (102) for amultimedia signal (101) in a database instead of the multimedia signalitself. To name a few: The memory/storage requirements for the databaseare reduced.

The comparison of fingerprints is more efficient than the comparison ofthe multimedia signals themselves, as fingerprints are substantiallyshorter than the signals.

Searching in a database for a matching fingerprint is more efficientthan searching for a complete multimedia signals, since it involvesmatching shorter items.

Searching for a matching fingerprint is more likely to be successful, assmall changes to a multimedia signal (such as encoding in a differentformat or changing the bit rate) do not affect the fingerprint.

Alternatively, if the multimedia content is in the form of more than asingle signal, e.g. a separate audio signal and a separate video signal,the fingerprint(s) (102) may be generated on the basis of a single ofthem (audio or video) or on both.

The generated fingerprints (102) stored in the database may then bedistributed to playback devices via the Internet or in a side-channel ofa broadcast channel or via some other channel or other means for useduring playback according to the present invention. As other examples ofdistribution is e.g. physical distribution on a storage medium or in anon-electronic way, e.g. requiring the user to enter the fingerprintsand actions manually into the playback device.

In a preferred embodiment, a representation of the associated action(s)is also stored for each fingerprint in the database. Theserepresentations are preferably also sent to the playback devices. In analternative embodiment, representations are not stored in the databaseor used at all when generating the fingerprints, Another party may thenprovide the representations to the relevant playback devices as well asa relationship between each fingerprint and its associated action(s).

FIG. 1b schematically illustrates detection and use of fingerprint(s) astrigger marker(s) according to the present invention. Shown is a digitalor analog multimedia signal (101) comprising video and/or audioinformation/content, where the signal (101) is played back by a suitableplayback device. Further shown is a fingerprint stream (104) that isgenerated continuously or substantially continuously on the basis of themultimedia signal (101). Alternatively, the fingerprint stream (104) isgenerated in segments. The fingerprint stream (104) (or segments) iscompared with fingerprints (102) stored in a database. The storedfingerprints (102) generated as explained in connection with FIG. 1a ata production site. The database preferably also comprisesrepresentations of the one or more associated actions (105) for eachstored fingerprint (102). The stored fingerprints (102) are e.g.received via the Internet or in a side-channel of a broadcast channel orvia some other channel or other means from the distribution site. Therepresentations of the associated action(s) (105) may also be receivedlike this. In an alternative embodiment, the representations as well asa relationship between each fingerprint and its associated action(s)(105) are provided by another party.

When a match between a segment of the fingerprint stream (104) and agiven fingerprint (102) in the database is found the representation(s)of the associated action(s) (105) of that particular fingerprint (102)is retrieved and executed at the appropriate time point (T_(n);T_(n+1)). When a match between a segment of the fingerprint stream (104)and a fingerprint (102) in the database, the appropriate time point(T_(n); T_(n+1)) is also determined when the fingerprints (102) havebeen generated as explained in connection with FIG. 1a . Preferably, thegiven time point (T_(n); T_(n+1)) is determined by letting the segmentof the multimedia signal (101) that the matching fingerprint originallyhas been based on during generation (according to FIG. 1a ) endingsubstantially at the given time point (T_(n); T_(n+1)). In alternativeembodiments, the segment of the multimedia signal (101) may startsubstantially at the given time point (T_(n); T_(n+1)), the segment ofthe multimedia signal (101) is starting or ending at a predetermineddistance before or after the given trigger time point (T_(n); T_(n+1))or the given time point (T_(n); T_(n+1)) may be at a predetermined timepoint between a start and an end of the segment of the multimedia signal(101). The playback device simply needs to be aware of the relationshipbetween a given fingerprint and the given time point used duringgeneration.

When a matching fingerprint (102) is determined, the associated one ormore actions is also retrieved. The playback device may then executethese actions or present them to a user e.g. awaiting user confirmationbefore executing them.

The above-mentioned European patent application 01200505.4 describesvarious matching strategies for matching fingerprints computed for anaudio clip with fingerprints stored in a database.

Further European patent application 01202720.7 describes an efficientmethod of matching a fingerprint representing an unknown informationsignal with a plurality of fingerprints of identified informationsignals stored in a database to identify the unknown signal. This methoduses reliability information of the extracted fingerprint bits. Thefingerprint bits are determined by computing features of an informationsignal and thresholding said features to obtain the fingerprint bits. Ifa feature has a value very close to the threshold, a small change in thesignal may lead to a fingerprint bit with opposite value. The absolutevalue of the difference between feature value and threshold is used tomark each fingerprint bit as reliable or unreliable. The reliabilitiesare subsequently used to improve the actual matching procedure.

A further advantage of the present invention is that if for any reasonthe broadcast is delayed, the fingerprint matching ensures that thetrigger actions still appear at the correct corresponding moment in thebroadcast since the invention is time-independent but content-dependent.

FIG. 2 illustrates a schematic block diagram of a fingerprint generationdevice according to the present invention. Shown is fingerprintgeneration device (200) comprising a multi-media signal input module(201), a fingerprinting module (202), a data base, memory storage and/orthe like (203) communicating via a bus (205) or the like under thecontrol of one or more microprocessors (not shown). The fingerprintgeneration device (200) may in one embodiment optionally also comprise atransmitter and receiver (204) for communicating with other systems,devices, etc. via a wired and/or wireless network e.g. like theInternet.

The multi-media signal input module (201) receives multimedia contente.g. in the form of an analog or digital audio and/or video signal andfeeds the multimedia content to the fingerprinting module (202). Thefingerprinting module (202) computes a fingerprint on the basis of thereceived multi-media content. A fingerprint may be derived for theentire content or for a part of the content. Alternatively, severalfingerprints may be derived each from a different part. According to thepresent invention, a fingerprint is derived each time that a triggeraction is needed, i.e. for each time point (T_(n); T_(n+1)), asexplained in connection with FIG. 1a . A representation of the timepoint(s) is also supplied to the fingerprinting module (202).

The fingerprinting module (202) then supplies the computedfingerprint(s) to the database (203) preferably together with theassociated one or more actions for each fingerprint. As shown in FIG. 4,the database (203) comprises fingerprints ‘FP1’, ‘FP3’, ‘FPS’, etc. andrespective associated actions ‘A1’, ‘A2’, ‘A3’, ‘A4’, ‘A2, A1’, etc.

The database (203) can be organized in various ways to optimize querytime and/or data organization. The output of the fingerprinting module(202) should be taken into account when designing the tables in thedatabase (203). In the embodiment shown in FIG. 4, the database (203)comprises a single table with entries (records) comprising respectivefingerprints and associated (sets) of actions.

FIG. 3 illustrates a schematic block diagram of a playback devicedetecting and using fingerprints according to the present invention.Shown is a playback device (300) comprising a multimedia signal receiver(301), a fingerprint detector (302), a display/play circuit (303), adata base, memory storage and/or the like (203′) communicating via a bus(205) or the like under the control of one or more microprocessors (notshown). The playback device (300) may in one embodiment optionally alsocomprise a transmitter and receiver (204) for communicating with othersystems, devices, etc. via a wired and/or wireless network e.g. like theInternet.

The multimedia signal receiver (301) receives the multimedia signal e.g.in the form of an analog or digital audio and/or video signal to bedisplayed and/or played e.g. from a broadcasting cable, antenna,satellite dish, etc. arrangement (not shown). The received multimediasignal is fed to the fingerprint detector (302) that derives afingerprint stream or segments thereof and determines if there are anymatches with fingerprints stored in the database as explained inconnection with FIG. 1b . If a match is found then a representation ofthe associated action(s) is also retrieved. The appropriate time pointfor the associated action(s) is given by the matching fingerprint asdescribed above.

The received multimedia signal is displayed and/or played by the adisplay/play circuit (303) and at the appropriate time point(s) theassociated action(s) is executed or presented to a user e.g. awaitinguser confirmation before executing the action(s).

Preferably, the data layout of the database (203′) corresponds to theone shown in FIG. 4.

The playback device (300) may also comprise a buffer mechanism (notshown) for buffering a part of the multimedia signal beforedisplaying/playing it.

FIG. 4 illustrates one example of tables/records according to thepresent invention. Shown is a table comprising fingerprints (102) ‘FP1’,‘FP2’, ‘FP3’, ‘FP 4’, ‘FP5’, etc. and respective associated actions(105) ‘A1’, ‘A2’, ‘A3’, ‘A4’, ‘A2, A1’, etc. One or more actions (105)are stored for each fingerprint (102). A given fingerprint (102) is onlystored in the table once.

In the claims, any reference signs placed between parentheses shall notbe constructed as limiting the claim. The word “comprising” does notexclude the presence of elements or steps other than those listed in aclaim. The word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements.

The invention can be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means canbe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

The invention claimed is:
 1. A method comprising: receiving, by a signalreceiver of a media playback device, a first media stream; playing back,on a display associated with the media playback device, the first mediastream; determining, by a processor of the media playback device, atrigger fingerprint from a segment of the first media stream, whereinthe trigger fingerprint is a representation of features of the segment;matching the trigger fingerprint to a reference fingerprint, wherein thereference fingerprint is stored in a database of reference fingerprintsand is associated with a reference action, and wherein the referenceaction: is associated with a time point indicating when, in the firstmedia stream, the reference action is to be performed; and instructs themedia playback device to replace playback of the first media stream withplayback of a second media stream; and responsive to matching thetrigger fingerprint to the reference fingerprint, playing back, on thedisplay associated with the media playback device, the second mediastream in place of the first media stream.
 2. The method of claim 1,wherein the playing back of the second media stream in place of thefirst media stream occurs at the time point.
 3. The method of claim 1,wherein the trigger fingerprint is one of a plurality of triggerfingerprints determined from respective segments of the first mediastream.
 4. The method of claim 1, further comprising: before determiningthe trigger fingerprint, receiving, by the media playback device, aplurality of reference fingerprints that includes the matched referencefingerprint.
 5. The method of claim 4, further comprising: storing thereceived reference fingerprints at the media playback device forcomparison with the trigger fingerprint.
 6. The method of claim 5,further comprising: receiving, by the media playback device, for each ofthe received reference fingerprints, representations of one or moreactions with which the received reference fingerprint is associated; andstoring each of the received representations in association with itsrespectively associated reference fingerprint.
 7. A method comprising:receiving, by a signal receiver of a computing system, a first mediastream; determining, by a processor of the computing system, a referencefingerprint from a segment of the first media stream, the referencefingerprint associated with a reference action that is associated with atime point that indicates when, in the first media stream, the referenceaction is to be performed; and transmitting, by the processor of thecomputing system, the reference fingerprint and the reference action toa media playback device, wherein reception of the reference fingerprintand the reference action result in the media playback device: matchingthe reference fingerprint to a trigger fingerprint, wherein the triggerfingerprint was generated by the media playback device during playbackof the segment of the first media stream, and wherein the triggerfingerprint is a representation of features of the segment of the firstmedia stream; and performing the reference action, wherein performanceof the reference action causes the media playback device to play back asecond media stream in place of the first media stream.
 8. The method ofclaim 7, wherein the playing back of the second media stream in place ofthe first media stream occurs at the time point.
 9. The method of claim7, wherein the trigger fingerprint is one of a plurality of triggerfingerprints determined from respective segments of the first mediastream.
 10. The method of claim 7, further comprising: beforedetermining the trigger fingerprint, transmitting, to the media playbackdevice, a plurality of reference fingerprints that includes the matchedreference fingerprint.
 11. The method of claim 10, wherein: storage ofthe transmitted reference fingerprints at the media playback device forcomparison with the trigger fingerprint results.
 12. The method of claim10, further comprising: transmitting, to the media playback device, foreach of the transmitted reference fingerprints, representations of oneor more actions with which the transmitted reference fingerprint isassociated.
 13. A media playback device comprising: a memory that storesinstructions; a database that stores reference fingerprints andreference actions; a media signal receiver configured to receive a firstmedia stream; one or more processors configured by the instructions toperform operations comprising: playing back, on a display, the firstmedia stream; determining a trigger fingerprint from a segment of thefirst media stream, wherein the trigger fingerprint is a representationof features of the segment; matching the trigger fingerprint to areference fingerprint stored in the database, wherein the referencefingerprint is associated with a reference action, and wherein thereference action: is associated with a time point indicating when, inthe first media stream, the reference action is to be performed; andinstructs the media playback device to replace playback of the firstmedia stream with playback of a second media stream; and responsive tomatching the trigger fingerprint to the reference fingerprint, playingback, on the display, the second media stream in place of the firstmedia stream.
 14. The media playback device of claim 13, wherein theplaying back of the second media stream in place of the first mediastream occurs at the time point.
 15. The media playback device of claim13, wherein the trigger fingerprint is one of a plurality of triggerfingerprints determined from respective segments of the first mediastream.
 16. The media playback device of claim 13, wherein theoperations further comprise: before determining the trigger fingerprint,receiving, by the media playback device a plurality of referencefingerprints that includes the matched reference fingerprint.
 17. Themedia playback device of claim 16, wherein the operations furthercomprise: storing the received reference fingerprints at the mediaplayback device for comparison with the trigger fingerprint.
 18. Themedia playback device of claim 17, wherein the operations furthercomprise: receiving, by the media playback device, for each of thereceived reference fingerprints, representations of one or more actionswith which the received reference fingerprint is associated; and storingeach of the received representations in association with itsrespectively associated reference fingerprint.